This invention is generally directed to toner and developer compositions which are useful in electrostatograhic imaging systems. More specifically, the present invention is directed to toner and developer compositions containing polymeric charge enhancing additives, which additives function as charge control materials, and impart a positive charge to the toner composition. Additionally the use of these polymeric additives in developer compositions increases the admix charging rate of new uncharged toner particles added to charged developer compositions comprised of toner and carrier particles, present for example in a xerographic imaging apparatus. Furthermore, the polymeric charge enhancing additives of the present invention control the magnitude of the charge on the toner particles. Toners and developers containing the polymeric additives of the present invention are particularly useful in electrostatographic copying devices employing Viton fuser systems as more specifically detailed hereinafter.
The electrostatographic process and more specifically, the xerographic process is well known, as documented in several prior art references. In these processes, an electrostatic latent image is developed by applying toner particles to the image, using, for example, cascade development, magnetic brush development, or touchdown development. In some instances, it may be desirable in these systems to obtain a reverse copy from a positive original, or a positive copy from a negative original. This can be accomplished by modifying the charging relationships between the toner and the carrier particles, utilizing, for example, charge enhancing additives.
In U.S. Pat. No. 3,893,935, there is disclosed the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium salts when incorporated into toner materials were found to provide a toner composition which exhibited relatively high uniform and stable net toner charge, when mixed with a suitable carrier. U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is used, namely a diazo type compound.
There is also described in copending applications, and U.S. Pat. No. 4,298,672, charge enhancing additives, which are not only useful for imparting a positive charge to the toner resin, but also allow rapid admix of uncharged toner particles. One problem associated with some of these charge enhancing additives is that they have a tendency to adversely affect Viton coated fuser rolls, that is, toners containing such additives can react with the Viton coatings causing the rolls to malfunction, and thus result in inefficient fusing. Also, there is disclosed in the referred to copending applications and U.S. Patent, charge control additives that differ significantly from the polymeric additives of the present invention.
Additionally, several of the prior art developer compositions which contain charge enhancing additives have a tendency to lose their positive charge over a periof of time, and in some instances, the additives are incompatible with the thermoplastic toner resin, thus creating difficulties in achieving a uniform dispersion of such materials in the toner composition. Furthermore, when new uncharged replenishment toner particles are added to charged developer compositions the new particles do not acquire the desired positive charge until a substantial period of time has elapsed, and it is important in order to constantly obtain good quality images, as well as for other purposes, that the newly added toner particles rapidly acquire the appropriate positive charge. This is referred to as admix charging.
Accordingly there continues to be a need for positively charged toners and developers which will allow the production of high quality images over extended time periods. Additionally, there is a need for improved charge enhancing additives, which when added to toners and developers control the toner charge and admix rate of newly added uncharged toner particles. Further there is a need for toners and developers containing charge control additives that do not adversely affect certain fuser rolls, such as Viton coated fuser rolls used in xerographic imaging systems. Additionally, there continues to be a need for new charge enhancing additives.